1. Field of the Invention
This invention relates in general to storage devices, and more particularly to a method and apparatus for providing combined radial and timing multislot self-servowrite propagation.
2. Description of Related Art
Increased levels of storage capacity in floppy and hard disk drives are a direct result of the higher track densities possible with voice-coil and other types of servo positioners as well as the ability to read and write narrower tracks by using, for example, magnetoresistive (MR) head technology. An embedded servo is needed so that the position of the head can be determined from the signals it reads.
Conventional hard disk manufacturing techniques including writing servo tracks on the media of a head disk assembly (HDA) with a specialized servo writer instrument. Laser positioning feedback is used in such instruments to read the actual physical position of a recording head used to write the servo tracks. Unfortunately, it is becoming more and more difficult for such servo writers to invade the internal environment of a HDA for servo-writing because the HDAs themselves are exceedingly small and depend on their covers and castings to be in place for proper operation. Some HDAs are the size and thickness of a plastic credit card. At such levels of microminiaturization, traditional servo-writing methods are inadequate.
Conventional servo-patterns typically comprise short bursts of a constant frequency signal, very precisely located offset from a data track's centerline, on either side. The bursts are written in a sector header area, and can be used to find the centerline of a track. Staying on center is required during both reading and writing. Since there can be hundreds of sectors per track, that same number of servo data areas must be dispersed around a data track. These servo-data areas allow a head to follow a track center line around a disk, even when the track is out of round, as can occur with spindle wobble, disk slip and/or thermal expansion. As technology advances to provide smaller disk drives, and increased track densities, the placement of servo data must also be proportionately more accurate.
In magnetic disk drives, magnetic heads and recorded servo code in a track following servo mode are used for keeping the magnetic heads track centered during reading operations. The magnetic heads comprise a magnetic core having an air gap therein and having a coil wound thereon. These magnetic cores vary in effective magnetic widths due to their design and due to the manufacturing process. These physical variations among the magnetic heads result in variations in servo gain when they are individually connected in the servo loop.
During the manufacture of a magnetic disk drive it is necessary to provide a magnetic pattern on each surface of each disk that is used by the servo control system for position and timing feedback. This pattern is known as the servo pattern. The process of writing this servo pattern onto each disk is known as servo writing. Typically the servo writing process is done in a clean room environment before the magnetic disk drive is completely sealed. During the servo writing process it is necessary to have very accurate position and timing feedback so that the servo pattern can be properly written across the entire surface of each disk in the magnetic disk drive. The position feedback is typically provided by a positioner that comes in physical contact with the arms, which support the heads on each surface of the magnetic disk drive. The positioner provides the feedback and the ability to move the heads via the arms with sufficient accuracy. The arms are kept in contact with the positioner by applying a constant bias force against the positioner's pushpin.
The timing feedback is provided by writing a pattern circumferentially around the disk with a dedicated head known as a clock head. It is inserted over one of the disks in the magnetic disk drive for this purpose during the servo write process and then removed once the process is complete. The timing feedback has also been provided by writing timing signals with the heads in the magnetic disk drive equally spaced around the circumference of at least one disk. The timing signals, called timing marks, need to be written each time the position of the heads is changed.
There is a lot of interest in the magnetic disk drive business on being able to servo write a magnetic disk drive without any external position or timing feedback to assist in the servo writing process. This is generally referred to as self-servo writing. Self-servo writing allows the servo write process to be moved outside of the clean room after the magnetic disk drive has been sealed. This provides a great cost advantage because clean room space is very expensive. Likewise there has been an interest making this process more affordable by using the same electronics that are used on the finished product. In the product electronics the data channel is the primary source of position and timing feedback.
It can be seen that there is a need for a method and apparatus for simplifying the process of writing of a pattern onto the disk with sufficient accuracy for the servo writing process.